When playing long simulation/strategy games like SimCity, Roller
Coaster Tycoon, or Civilization, I often have “what if” questions:
what if I built an airport there? what if I invaded Albania? what if I
switched to solar power? what if I built extra police stations?

My usual answer is to just keep wondering. However if I'm very
motivated I can save the game, try something, save it again, go back
to the first save game, try the other option, and then compare the
results. It's rather tedious, so I don't do it much.

It might be interesting to bring the “what if” gameplay into the game
itself, instead of being outside of it, as save games. Games like
Chronotron and
Braid allow you to go back and try something
else, and even see past paths while you're playing through
again. Halo 3 heatmaps
aggregate information from a huge number of games. I think these ideas
apply to simulation/strategy games too.

Imagine if you could “split” the timeline into two and watch parallel
worlds evolve simultaneously:

If it's just a matter of running parallel worlds, I could do this by
running the game twice, in two side by side windows. However if it was
integrated into the game there's some potential for interesting gameplay:

The game could run two worlds all the time. Every 5 minutes the
game could ask you which world is better, and then copy that world
to both windows. You could run experiments but they're all limited
to 5 minutes. You'd be able to learn by experimentation and then
use that knowledge in the future.

The game could run one world most of the time, but then in a
world-splitting event, split into two. In one world you'd be asked
to destroy; in the other, to build. You'd gain bonus points for
maximizing the difference between the worlds.

The game could let you play in one window and show in the other
window the accumulated plays from your previous games on the same
map, or perhaps from other people's games. Differences in play
would be highlighted, and you'd gain points for novel play
styles. In Halo, you might get a bonus for a sniper shot from a
location where few people succeed making a sniper shot.

In a multiplayer setting, each player could play in her own
world for a few minutes, and then the game would ask everyone to
vote for their favorite world other than their own, and then that
world would become the baseline for the next round of play. It
might be possible to integrate this into a Facebook game that you
play asynchronously with your friends.

If playing against a computer AI, it might be fair to let the
computer player occasionally choose which world it prefers. The
strategy would then be to set up a world that appears to give you
a disadvantage without actually doing so. The Chess equivalent
would be to intentionally sacrifice a rook in order to set up a
winning move.

I'd love to see games explictly tackle parallel worlds, individually
and in aggregate.